Arrangement for recirculation of exhaust gases of a supercharged internal combustion engine

ABSTRACT

The present invention relates to an arrangement for recirculation of exhaust gases of a supercharged combustion engine. The arrangement comprises an exhaust line intended to lead exhaust gases out from the combustion engine, an inlet line intended to lead air which is at above atmospheric pressure to the combustion engine, a compressor adapted to the inlet line so that it is possible, via the return line, to recirculate exhaust gases from the exhaust line to the inlet line. The arrangement comprises a first EGR cooler in which the recirculating exhaust gases in the return line are cooled by the air in a portion of the inlet line which is situated downstream of the compressor in the inlet line with respect to the direction of flow of the air in the inlet line.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a 35 U.S.C. §§371 national phase conversionof PCT/SE2006/050108, filed May 5, 2006, which claims priority ofSwedish Patent Application No. 0501124-2, filed May 18, 2005, thedisclosure of which has been incorporated herein by reference.

BACKGROUND TO THE INVENTION, AND STATE OF THE ART

The present invention relates to an arrangement for recirculation ofexhaust gases of a supercharged combustion engine according to thepreamble of claim 1.

The technique known as EGR (Exhaust Gas Recirculation) is a known meansof leading part of the exhaust gases from a combustion process in acombustion engine back, via a return line, to an inlet line for supplyof air to the combustion engine. A mixture of air and exhaust gases isthus supplied via the inlet line to the engine's cylinders in which thecombustion takes place. Adding exhaust gases to the air causes a lowercombustion temperature which results inter alia in a reduced content ofnitrogen oxides NO_(x) in the exhaust gases. This technique is used forboth Otto engines and diesel engines.

Providing such recirculation of exhaust gases involves arranging areturn line in an engine space of the vehicle. The purpose of such areturn line is to lead the exhaust gases from an exhaust line arrangedon the warm side of the combustion engine to an inlet line for airarranged on the cold side of the combustion engine. The return linecomprises a plurality of components such as an EGR valve for controllingthe exhaust gas flow through the return line, an EGR cooler for coolingthe recirculating exhaust gases, and pipeline portions for leading theexhaust gases from the warm side to the cold side. The location of theEGR cooler in the vehicle is usually such that the return line has to beunnecessarily long and space-consuming.

The amount of air which can be supplied to a supercharged combustionengine depends on the pressure of the air but also on the temperature ofthe air. In order to supply as large an amount of air as possible to thecombustion engine, the compressed air is cooled in a charge air coolerbefore it is led to the combustion engine. The compressed air is cooledin the charge air cooler by ambient air which is led through the chargeair cooler. The compressed air can thus be cooled to a temperature whichexceeds the temperature of the surroundings by only a few degrees. Thereturned exhaust gases are usually cooled in an EGR cooler which usesthe coolant of the combustion engine's cooling system as cooling medium.Such an EGR cooler is therefore subject to the limitation that theexhaust gases cannot be cooled to a lower temperature than thetemperature of the coolant. The cooled exhaust gases are thereforeusually at a higher temperature than the cooled compressed air when theymix in the inlet line to the combustion engine. The mixture of exhaustgases and air which is led to the combustion engine will therefore be ata higher temperature than the compressed air which is led into acorresponding supercharged combustion engine without recirculation ofexhaust gases. The performance of a supercharged combustion engineequipped with EGR will thus be somewhat inferior to that of asupercharged combustion engine not equipped with EGR.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an arrangement whicheffects recirculation of exhaust gases of a combustion engine wherebythe return line can be of substantially minimum length and thearrangement as a whole be made compact and occupy little space. Anotherobject is to provide an arrangement which effects recirculation ofexhaust gases of a supercharged combustion engine whereby therecirculation of exhaust gases does not result in the performance of thecombustion engine being inferior to that of a corresponding combustionengine without recirculation of exhaust gases.

These objects are made possible by the arrangement of the kind mentionedin the introduction which is characterised by the features indicated inthe characterising part of claim 1. The compressed air in the inlet lineconstitutes an existing cooling medium source situated close to thecombustion engine. The EGR cooler which uses this cooling medium sourcecan therefore be fitted in direct proximity to or on the combustionengine. The return line which comprises such an EGR cooler can thereforebe made short and compact so that the exhaust gases undergo only a smallpressure drop as they pass through the return line. A small pressuredrop in the return line is necessary for being able to achieve low fuelconsumption and for ensuring that exhaust gases can without problems beled into the inlet line and mix with the compressed air in the inletline. As the compressor already draws in and conveys air in the inletline, no further flow devices need usually be applied in the inlet linein order to provide a flow of air through the EGR cooler. It istherefore relatively uncomplicated to arrange close to the combustionengine such an EGR cooler which uses this already existing air flow inthe inlet line downstream of the compressor in order to cool the exhaustgases in the return line. The compressed air in the inlet line may be ata temperature of up to 290° C. However, the temperature of thecompressed air is considerably lower than the temperature of the exhaustgases, which may be around 600-700° C. The compressed air in the inletline can therefore be used in an EGR cooler to provide a first step ofcooling for the exhaust gases.

According to a preferred embodiment of the present invention, thearrangement comprises a second EGR cooler adapted to providing therecirculating exhaust gases in the return line with a second step ofcooling after they have been cooled in the first EGR cooler. It is ofcourse not sufficient merely to cool the exhaust gases in a first EGRcooler by means of compressed air when it is at such a high temperature.The recirculating exhaust gases are with advantage adapted to beingcooled in the second EGR cooler by a medium which is at the temperatureof the surroundings. With a suitably dimensioned EGR cooler it istherefore possible to cool the exhaust gases to a temperature close tothe temperature of the surroundings.

According to another preferred embodiment of the present invention, therecirculating exhaust gases in the return line are adapted to beingcooled in the second EGR cooler by the air in a portion of the inletline which is situated upstream of the compressor. The second EGR coolercan therefore also be fitted in direct proximity to or on the combustionengine. The return line comprising two such EGR coolers can thus be madevery short and compact so that the exhaust gases undergo only a verysmall pressure drop as they pass through the return line. Withadvantage, the air drawn into the inlet line is ambient air. Air at atemperature substantially corresponding to the temperature of thesurroundings can thus be used for cooling the exhaust gases in thesecond EGR cooler.

According to another preferred embodiment of the invention, thearrangement comprises a charge air cooler adapted to cooling thecompressed air in the inlet line to the combustion engine. Thecompressed air will be at a relatively high temperature after thecompression. When it has been used for cooling the exhaust gases, theair will be at a still higher temperature. The amount of air which canbe supplied to a supercharged combustion engine depends on the pressureand temperature of the air. In order to supply as large an amount of airas possible to the combustion engine, the compressed air needs toundergo effective cooling in the charge air cooler before it is led intothe combustion engine. With advantage, the compressed air is adapted tobeing cooled in the charge air cooler by a medium which is at thetemperature of the surroundings. The compressed air can thus be cooledto a temperature only a few degrees above the temperature of thesurroundings. Said medium is preferably ambient air. Ambient air issuitable for the purpose since it is always available and can easily becaused to flow through the charge air cooler.

According to another preferred embodiment of the invention, the chargeair cooler and a radiator for the combustion engine's cooling system arefitted in a common region through which ambient air flows. Such a regionmay be at a front portion of a vehicle which is powered by saidcombustion engine. Here a common radiator fan may be used forcirculating ambient air through both the charge air cooler and theradiator. The charge air cooler is preferably fitted upstream of theradiator in said common region with respect to the direction of flow ofthe air. Ambient air thus flows through the charge air cooler beforeflowing through the radiator. There is thus assurance of the compressedair being cooled by air which is at the temperature of the surroundings,thereby making it possible to cool the compressed air to a temperatureclose to the temperature of the surroundings. The ambient air flowingthrough the radiator thereby acquires a somewhat higher temperature, butthis temperature is sufficient for the coolant to undergo effectivecooling in the radiator.

BRIEF DESCRIPTION OF THE DRAWING

A preferred embodiment of the invention is described below by way ofexample with reference to the attached drawing, in which:

FIG. 1 depicts an arrangement for recirculation of exhaust gases of asupercharged combustion engine

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 depicts an arrangement for recirculation of exhaust gases of asupercharged combustion engine. The combustion engine in this case is adiesel engine 1. Such recirculation is usually called EGR (Exhaust GasRecirculation). Adding exhaust gases to the compressed air which is ledto the engine's cylinders lowers the combustion temperature and hencealso the content of nitrogen oxides (NO_(x)) formed during combustionprocesses. The diesel engine 1 may be intended to power a heavy vehicle.The exhaust gases from the cylinders of the diesel engine 1 are led viaan exhaust manifold 2 to an exhaust line 3. The exhaust gases in theexhaust line 3, which are at above atmospheric pressure, are led to aturbine 4. The turbine 4 is thus provided with driving power which istransmitted, via a connection, to a compressor 5. Via an air filter 6,the compressor 5 draws ambient air into a first portion 7 a of an inletline 7. The air is compressed by the compressor 5, with the result thatit reaches above atmospheric pressure and a relatively high temperature.Downstream of the compressor 5, the compressed air is led through asecond portion 7 b of the inlet line. A charge air cooler 8 is arrangedin the second portion of the inlet line 7 b in order to cool thecompressed air. The compressed air is cooled in the charge air cooler 8by ambient air which is caused to flow through the charge air cooler 8by a radiator fan 9. The radiator fan 9 is driven by the diesel engine 1via a suitable connection.

An arrangement for effecting recirculation of part of the exhaust gasesin the exhaust line 3 comprises a return line 10 which extends betweenthe exhaust line 3 and a third portion 7 c of the inlet line 7. Thereturn line 10 comprises an EGR valve 11 by which the exhaust flow inthe return line 10 can be shut off as necessary. The EGR valve 11 canalso be used for controlling the amount of exhaust gases led from theexhaust line 3 via the return line 10 to the third portion 7 c of theinlet line. A control unit 12 is adapted to controlling the EGR valve 11on the basis of information about the prevailing operating state of thediesel engine 1. The control unit 12 may be a computer unit providedwith suitable software. The return line 10 comprises a first EGR cooler13 a in which the exhaust gases undergo a first step of cooling and asecond EGR cooler 13 b in which the exhaust gases undergo a second stepof cooling. In certain operating states, the pressure of the exhaustgases in the exhaust line 3 of a supercharged combustion engine is lowerthan the pressure of the compressed air in the second portion 7 b of theinlet line. In such operating situations it is not possible to mix theexhaust gases in the return line 10 directly with the compressed airfrom the second portion 7 b of the inlet line without special auxiliarymeans. A venturi 14 may for example be used for the purpose. If thecombustion engine is a supercharged Otto engine, however, the exhaustgases in the return line 10 can usually be mixed directly with the airfrom in the second portion 7 b of the inlet line, since the exhaustgases in the exhaust line 3 of an Otto engine in substantially alloperating states are at a higher pressure than the compressed air in thesecond portion 7 b of the inlet line. When the exhaust gases have mixedwith the compressed air from the second portion 7 b of the inlet line,the mixture is led to the respective cylinders of the diesel engine 1via the third portion 7 c of the inlet line and a manifold 15.

The diesel engine 1 is cooled in a conventional manner by a coolingsystem with a coolant which is circulated by a coolant pump 16. Thecooling system also comprises a thermostat 17 and a radiator 18. Theradiator 18 is situated behind the charge air cooler 8 in the firstregion A, which has ambient air flowing through it. During operation ofthe diesel engine 1, the exhaust gases in the exhaust line 3 drive theturbine 4 before they are led out to the environment. The turbine 4 isthus provided with driving power which drives the compressor 5. Thecompressor 5 thus compresses the ambient air in the first portion 7 a ofthe inlet line. The compressed air in the second portion 7 b of theinlet line is cooled by ambient air which flows through the charge aircooler 8. The compressed air in the charge air cooler 8 is thus cooledto a temperature which exceeds the temperature of the surroundings byonly a few degrees.

In most operating states of the diesel engine 1, the control unit 12keeps the EGR valve 11 open so that part of the exhaust gases in theexhaust line 3 is led into the return line 10. The exhaust gases in theexhaust line 3 are at a temperature of about 600-700° C. When theexhaust gases in the return line 10 are led into the first EGR cooler 13a, they undergo cooling by the air in the second portion 7 b of theinlet line. However, the first EGR cooler 13 a is subject to thelimitation that it can at most cool the exhaust gases to the temperatureof the compressed air. The temperature of the compressed air may be upto 290° C. The exhaust gases nevertheless undergo with advantage arelatively large temperature reduction in the first EGR cooler 13 a sothat they are at a temperature of about 300° C. when they leave thefirst EGR cooler 13 a. The amount of compressed air and exhaust gaseswhich can be supplied to the diesel engine 1 depends on the pressure andtemperature of the air and the exhaust gases. It is therefore importantto provide further cooling of the recirculating exhaust gases. Theexhaust gases are therefore subjected in the second EGR cooler 13 b to asecond step of cooling by the air in the first portion 7 a of the inletline before it is compressed by the compressor 5. The air in the firstportion 7 a of the inlet line is at substantially the temperature of thesurroundings. By suitable dimensioning of the second EGR cooler 13 b,the exhaust gases undergo a second step of cooling to a temperature onlya few degrees above the temperature of the surroundings. The air flowingin the inlet line constitutes an existing cooling medium source situatedclose to the combustion engine 1. The first EGR cooler 13 a and thesecond EGR cooler 13 b can therefore be fitted in direct proximity to oron the combustion engine 1. The return line 10 can thus be made veryshort and compact so that the exhaust gases undergo only a smallpressure drop in the return line 10. A small pressure drop in the returnline 10 is necessary for being able to achieve low fuel consumption andfor ensuring that the exhaust gases can without problems be led into thereturn line 10 and mix with the compressed air from the second portion 7b of the inlet line.

The charge air cooler 8 and the cooling system's radiator 18 are thussituated in a common region A through which ambient air flows. Theregion A may be a region at a front portion of a vehicle which ispowered by the combustion engine 1. The charge air cooler 8 is fitted infront of the radiator 18 to ensure that air which is at the temperatureof the surroundings flows through it and cools it. By suitabledimensioning of the charge air cooler 8, the air in the charge aircooler 8 can thus be cooled to a temperature close to the temperature ofthe surroundings. The air which cools the coolant in the radiator 18thus acquires a temperature which is somewhat higher than thesurroundings but is usually quite sufficient for cooling the coolant inthe radiator 18, since there is no need for the coolant in the radiator18 to be cooled to a temperature equal to the temperature of thesurroundings. The air in the inlet line is thus used for cooling theexhaust gases in the first EGR cooler 13 a and the second EGR cooler 13b. The air in the inlet line thus acquires a raised temperature beforeit reaches the charge air cooler. The charge air cooler 8 thereforeneeds a somewhat greater capacity to be able to cool away this extraheat.

In certain operating states of a supercharged combustion engine 1, thepressure of the exhaust gases in the exhaust line 3 is thus lower thanthe compressed air pressure from the second portion 7 b of the inletline. It is possible, e.g. by means of said venturi 14, for the staticpressure from the second portion 7 b of the inlet line to be reducedlocally, at the connection to the return line 10, so that the exhaustgases can be led into and mix with the compressed air in the thirdportion 7 c of the inlet line. The mixture of exhaust gases andcompressed air is thereafter led to the respective cylinders of thediesel engine 1 via the manifold 15. By such cooling in two steps in theEGR coolers 13 a, b it is thus possible for a diesel engine 1 equippedwith EGR to be provided with recirculating exhaust gases at atemperature substantially corresponding to the temperature of thecompressed air after it has been cooled in the charge air cooler 8. Themixture of exhaust gases and compressed air which is led to the dieselengine 1 will thus be at a temperature substantially corresponding tothat of the compressed air which is led to a diesel engine without EGR.The present invention thus makes it possible for a diesel engineequipped with EGR to present performance substantially corresponding tothat of a diesel engine not equipped with EGR.

The invention is in no way limited to the embodiments described withreference to the drawing but may be varied freely within the scopes ofthe claims.

1. An arrangement for recirculation of exhaust gases of a superchargedcombustion engine, the arrangement comprising: an exhaust lineconfigured to lead exhaust gases out from the combustion engine; aninlet line configured to lead air from a compressor to a first EGRcooler and then from the first EGR cooler to the combustion engine; thecompressor configured to compress the air in the inlet line to aboveatmospheric pressure, and a return line which connects the exhaust lineto the inlet line so that the return line recirculates exhaust gasesfrom the exhaust line to the inlet line; the first EGR cooler positionedat the inlet line and configured to cool the recirculating exhaust gasesin the return line using the air in the inlet line; and a second EGRcooler positioned at the inlet line and configured to cool therecirculating exhaust gases in the return line after the recirculatingexhaust gases in the return line have been cooled in the first EGRcooler.
 2. The arrangement according to claim 1, wherein the second EGRcooler is positioned and configured to cool the recirculating exhaustgases using a medium at the temperature of the surroundings.
 3. Thearrangement according to claim 1, wherein the second EGR cooler ispositioned and configured to cool the recirculating exhaust gases in thereturn line using the air in a portion of the inlet line upstream of thecompressor with respect to the direction of air flow in the inlet line.4. An arrangement for recirculation of exhaust gases of a superchargedcombustion engine, the arrangement comprising: an exhaust lineconfigured to lead exhaust gases out from the combustion engine; aninlet line configured to lead air from a compressor to a first EGRcooler and then from the first EGR cooler to the combustion engine; thecompressor configured to compress the air in the inlet line to aboveatmospheric pressure, and a return line which connects the exhaust lineto the inlet line so that the return line recirculates exhaust gasesfrom the exhaust line to the inlet line; the first EGR cooler positionedat the inlet line and configured to cool the recirculating exhaust gasesin the return line using the air in the inlet line; and a charge aircooler positioned and configured to cool the compressed air in the inletline.
 5. The arrangement according to claim 4, wherein the charge aircooler is configured to cool the air in the inlet line by a medium whichis at the temperature of the surroundings.
 6. The arrangement accordingto claim 5, wherein the medium used by the charge air cooler is ambientair.
 7. The arrangement according to claim 6, wherein the charge aircooler is positioned in a region through which ambient air flows and theregion is shared by a radiator for a cooling system of the combustionengine.
 8. The arrangement according to claim 7, wherein the charge aircooler is positioned upstream of the radiator in the region with respectto the direction of flow of the ambient air.
 9. The arrangementaccording to claim 4, wherein the charge air cooler is positioned at theinlet line downstream, with respect to a direction of flow of the air inthe inlet line, of the first EGR cooler.
 10. The arrangement accordingto claim 4, wherein the charge air cooler is positioned downstream ofthe first EGR cooler and upstream, with respect to a direction of flowof the air in the inlet line, of a valve for combining the air in theinlet line with the exhaust gases.